1. Field of the Invention
The present invention relates to a method of conveying PTPs (press-through packs) for tablets or the like and, more specifically, to a PTP conveying method which selects, inverts and conveys some of a plurality of PTPs being conveyed, and a PTP conveying apparatus for carrying out the PTP conveying method.
2. Description of the Related Art
Referring to FIG. 1, a generally known PTP 1 has a plastic sheet 2 provided with a plurality of blisters 2a in one surface thereof (hereinafter, referred to as "blistered surface"), tablets 3 or such are put in the blisters 2a, and the blisters 2a containing the tablets 3 are sealed hermetically by a sheet 4, such as an aluminum foil.
A plurality of such PTPs are superposed in a stack, the stack is bundled with a band, packed in a film or put in a packaging box. When superposing the even number of PTPs, two adjacent PTPs are put one on top of the other with the blistered surfaces thereof facing each other, and the PTPs are dislocated from each other as shown in FIG. 2 so that the blisters 2a of one of the two PTPs are fitted in spaces between the blisters 2a of the other PTP to form the stack of the PTPs in a smaller thickness. When an odd number of such PTPs, i.e., three or more PTPs, are superposed, an even number of PTPs are superposed in the foregoing manner, and the last PTP is placed on the sheet 4 of the uppermost PTP of the stack of the even number of PTPs with its blisters 2a in contact with the sheet 4 of the uppermost PTP or with its sheet 4 in contact with that of the uppermost PTP.
Some of a plurality of PTPs being conveyed in one direction need to be inverted automatically and the inverted PTPs need to be put on the rest of the PTPs, i.e., uninverted PTPs, being conveyed to superpose the plurality of PTPs automatically. The present applicant proposed previously an automatic apparatus for this purpose in Japanese Patent Laid-open Publication Nos. 7-2358 and 7-2359. The aforesaid automatic apparatus comprises a conveying unit for intermittently conveying PTPs arranged with their blistered surfaces provided with blisters extended horizontally, and an automatic inverting unit disposed at the rear terminal end of the conveying unit. A turning means included in this automatic inverting unit comprises a rotary drum and a plurality of rotatable pinching means attached to the rotary drum so as to extend radially. The intermittently conveyed PTPs are subsequently clamped by the pinching means. While the rotary drum is turning through an angle of 180.degree., the pinching means are rotated about their axes to convey PTPs to a transfer position. The adjacent pinching means are driven for turning through angles of 360.degree. and 540.degree., respectively, by a gear train consisting of a planetary bevel gear and a fixed bevel gear while the rotary drum is turned through an angle of 180.degree.. A first PTP pinched by a first pinching means at the rear terminal end of the conveying unit with its blistered surface facing up and is transferred to a combining unit with its blistered surface facing up because the pinching means turns through an angle of 360.degree., and a second PTP following the first PTP is transferred to the combining unit with its blistered surface facing down because the pinching means holding the second PTP is turned through an angle of 540.degree.. Thus, the successive PTPs are combined by the combining unit in pairs of PTPs each of a PTT with its blistered surface facing up and a PTP with its blistered surface facing down, and the pairs of PTPs are delivered to a predetermined position.
A PTP package may contain a stack of an even number of PTPs or an odd number of PTPs, such as three, five or seven PTPs, stacked in the foregoing manner. The automatic inverting unit delivers the inverted PTPs and uninverted PTPs alternately to a transfer position. Therefore, if three successive PTPs are superposed in a stack, an uninverted PTP, an inverted PTP and an uninverted PTP are superposed in that order to form a first stack, and an inverted PTP, an uninverted PTP and an inverted PTP are superposed in that order to form a second stack. Thus, when an odd number of PTPs are superposed to form a stack, stacks of different structures are formed alternately. The stacks of the different structures result in differently structured packages, respectively, and may possibly cause problems in combining the inverted and uninverted PTPs and packaging the stacks of PTPs in subsequent steps.
Accordingly, when combining an odd number of PTPs by the prior art automatic inverting apparatus, the automatic inverting unit needs a special pinching means capable of arranging the odd number of PTPs in a predetermined positional relation. For example, when superposing three PTPs, the number of the pinching means of the rotary drum needs to be a multiple of three, and the pinching means must operate so that the first pinching means sets a first PTP with its blistered surface facing up, the second pinching means sets a second PTP with its blistered surface facing down and the third pinching means sets a third PTP with its blistered surface facing down. The automatic inverting unit needs a more complicated mechanism to combine five or seven PTPs in a set.
The rotary drum of the prior art automatic inverting unit is provided with a plurality of pinching means arranged so as to extend radially, and the adjacent pinching means turn the PTPs through different angles, respectively. Therefore, the prior art automatic inverting unit is complicated and costly, and it is very difficult to operate the prior art automatic inverting unit intermittently at a high operating speed.
In inverting an odd number of PTPs to form a predetermined arrangement, the number and turning angles of the pinching means for turning, for example, three PTPs through different angles, and those of the pinching means for turning five PTPs through different angles are different from each other. Therefore, the automatic inverting unit must be replaced as a whole with another one when the number of PTPs to be superposed is changed, and different automatic inverting units respectively for arranging PTPs to superpose different numbers of PTPs must be kept in reserve, which is costly and requires a troublesome adjusting operation for properly timing the operation of the automatic inverting unit so that the inverting unit may operate in synchronism with the conveying unit when replaced with the old unit which has been used in combination with the aforesaid conveying unit.